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Backgrground: The purpose of this study was to evaluate the reactogenicity and immunogenicity of a hepatitis A vaccine (Havrix-1440TM) when administered simultaneously with a Vi polysaccharide typhoid vaccine.

Methods: Two open, randomized studies were conducted using 2 and 4 treatment groups respectively, at the Clinique Notre-Dame de Grâce, Belgium (Study 1) and University Hospital of Hradec Kralové, Czech Republic (Study 2). Subjects: Healthy adults aged 18–50 years were administered either both vaccines concomitantly in separate arms or a single injection of the two vaccines mixed extemporaneously (Study 1), or one injection of each vaccine alone, or the combined vaccine, or both vaccines concomitantly in separate arms (Study 2). The study measured solicited and unsolicited signs and symptoms until 28 days post-vaccination. Anti-hepatitis A and anti-Vi titers were determined in pre- and post-vaccination sera.

Results: The vast majority of local and general symptoms were mild to moderate and all resolved without sequelae. No serious adverse events were reported in either study. In study 1, geometric mean antibody titers (GMTs) were similar after extemporaneous syringe mixing of both vaccines (anti-Vi = 1159 EL.U/mL; anti-HAV = 302 EL.U/mL) and after concomitant vaccination (anti-Vi = 1331 EL.U/mL; anti-HAV = 367 EL.U/mL). In study 2, GMTs following vaccination with either vaccine alone, both vaccines administered concomitantly or as a combined vaccine (anti-Vi: 1307, 1247 and 942 EL.U/mL, respectively; anti-HAV: 462, 517 and 432 EL.U/mL, respectively) were not significantly different (p = .45 for anti-HAV, p = .18 for anti-Vi). Seroconversion rates were > 94.4% in all cases.

Conclusions: The inactivated hepatitis A and Vi polysaccharide typhoid vaccines are safe and well tolerated when administered simultaneously (mixed or concomitant) and as a combined vaccine. Subjects seroconverted to both antigens to the same extent as the monovalent vaccines and there was no cross-interference in the immune profiles of the vaccines.